I. Field of the Invention
The present invention relates generally to valve actuators, and more particularly, to a novel drive engagement between the valve actuator and a valve rotatable member wherein the axis of rotation of the actuator is offset from the axis of rotation of the rotatable member.
II. Description of the Prior Art
There are a wide variety of different types of valves used throughout industry, and likewise, a plurality of previously known valve actuators for each of the different types of valves. In the "rising stem" type of valve, which is commonly used as an oil pipeline valve or the like, a rotatable member threadably engages an elongated valve stem. The rotatable member is fixed against axial movement, while conversely, the valve stem is fixed against rotational movement so that rotation of the rotatable member axially moves the valve stem to actuate the valve.
In order to actuate the so called "rising stem" valves, it has been the previous practice to connect a hand wheel, crank or the like to the rotatable member in order to effect rotation thereof. These valve actuators, however, have proven disadvantageous in that the valve stem is subjected to wear and tear from the natural elements, and even to vandalism. Moreover, it has been found that repeated attachment and removal of the actuating wheel tends to damage the valve stem as the hand actuators bang against the valve stem due to carelessness of the workmen. Lastly, since the valve stem moves axially through the center of the hand wheel, the valve stem itself tends to interfere with the natural cranking action of the workmen.
In order to solve these difficulties, more complex valve actuators have been devised in which a gear arrangement is provided for drivingly engaging the rotatable member and wherein the valve stem is received in an elongated recess. These previously known valve actuators, however, have also proven disadvantageous in several ways. First, since the axial travel of the valve stems varies from one valve to another, it has been the previous practice to produce an entire line of valve actuators having different sizes of elongated recesses for receiving the valve stems but which are otherwise substantially identical. This necessity of manufacturing or stocking a line of actuators unnecessarily increases the tooling and warehousing costs for the valve actuators.
A still further disadvantage of these previously known valve actuators is that the valve actuators are unnecessarily complex and require extensive tooling during their production, which of course, increases the costs of the actuator. In particular, many previously known valve actuators utilize an interdigital clutch mechanism between the actuator and the valve rotatable member for drivingly engaging the same. The previously known interdigital clutch is not only expensive to manufacture, but is also prone to failure. Moreover, many of these previously known valve actuators require extensive modifications of the valve which is not only expensive but oftentimes impractical, particularly when the valve is already installed in the field.